1. Field of the Invention
The invention relates to the art of induction melting of metals and alloys. The invention is directed to a melting liner or crucible used in conjunction with a backup crucible in an induction melting furnace.
2. Description of Related Art
In induction melting furnaces, a melting liner is used to hold metals during a melting process. A backup crucible surrounds the melting liner for safety purposes. If there is a failure in the melting liner, the backup crucible captures any molten metal that may escape the melting liner, thereby protecting the induction furnace from damage. The melting liner and backup crucible are manufactured and used as matched sets.
The backup liner is cemented into the induction furnace and a matched melting liner is inserted into the backup crucible. The melting liner is matched to the backup crucible in the sense that the melting liner must protrude a predetermined distance beyond the backup liner. Additionally, the melting liner should be received within the backup crucible with a minimum of play, or space, between the melting liner and the backup crucible. The melting liner must protrude a specified distance above the backup liner to permit an uncontaminated, free flowing pour, of the molten metal out of the liner and into, for example, a mold. If the molten metal makes contact with the backup crucible, undesirable inclusions may be introduced into the metal. Additionally, metal contact with the backup crucible can disrupt the direction and flow characteristics of the molten metal into the mold, causing, for example, dangerous and wasteful spills. The predetermined protrusion distance, or the height differential between the top of the backup crucible and the top of the melting liner is referred to as the xe2x80x9cfree lipxe2x80x9d distance.
When the mold capacity and/or the alloy to be melted changes, the melting liner must be changed to accommodate the larger/smaller charge weight and/or to eliminate the possibility of metal contamination from one alloy to another. Mold capacity fluctuates from ounces to hundreds of pounds. The alloys used vary widely. To accommodate the new melting liner, a matching backup crucible is also installed. For example, in order to achieve a proper free lip dimension when a shorter melting liner is used, the existing backup crucible is removed and a new backup crucible of the proper height is installed that corresponds to the reduction in height of the melting liner. The removal of the old backup crucible and installation of the new backup crucible is a time consuming task that can take up to 8 or more hours to complete. It is desirable to eliminate this labor expense. Furthermore, backup crucible changeovers interrupt production. The reduction in profits due to lost production can be even more significant than the changeover labor costs. Therefore, production managers are pressured to reduce the frequency of changeovers. Consequently, long production runs of the same capacity molds and/or alloy are scheduled. This means that product is stored in warehouses rather than being manufactured xe2x80x9cjust in timexe2x80x9d for delivery to a customer. Warehousing a product is expensive. Additionally, one risks producing product than may never be sold. Therefore, there are also pressures to produce product on a just-in-time basis.
An alternative to changing out the backup liner is to use an appropriately sized pedestal placed in the bottom of the backup crucible. For example, the pedestal raises the height of a small melting liner in order to provide the required free lip dimension. A different pedestal is required for each melting liner size to maintain the proper free lip distance. Although more cost effective than backup crucible removal, the use of pedestals is cumbersome in practice. Pedestal use involves stocking and inventorying additional components (the pedestal), selecting the correct pedestal for each new melting liner and installing and aligning the pedestal. Additionally, pedestals tend to fall out of the backup crucible at the end of a pour, adding to the risk of mold disruption. In general, pedestal use is found to be so cumbersome, that the most common practice is to change the backup crucible instead of using pedestals.
In order to reduce change over labor and downtime, a new liner system has been developed. The new liner system includes a melting liner operative to hold a charge of metal and to be received within a backup crucible of an induction melting furnace. The melting liner comprises a basin portion sized appropriately for an intended size charge, and an integral foot portion sized to hold a lip of the basin portion in a predetermined position relative to a lip of the backup crucible.
When the required mold capacity and/or the alloy to be processed changes, a backup liner in the furnace is not removed. Instead, only an old melting liner is removed. An appropriately sized melting liner with an appropriately sized integral foot or integral pedestal is then received within the backup crucible.
One advantage of the present invention resides in a reduction in production downtime needed to remove and replace the backup crucible, or retrieve and install an appropriate pedestal.
Another advantage of the present invention is a reduction in change over labor costs.
Yet another advantage of the present invention is found in productivity and manufacturing flexibility enhancement, which eliminates the need for long mold runs.
Still other advantages of the present invention will be apparent to those of ordinary skill in the art upon reading and understanding the following detailed description and viewing drawings associated therewith.